/Engine/Source/Runtime/Engine/Public/GeomTools.h
Take the input mesh and cut it with supplied plane, creating new verts etc. Also outputs new edges created on the plane.
namespace FGeomTools { void FGeomTools::ClipMeshWithPlane ( [TArray](API\Runtime\Core\Containers\TArray)< [FClipSMTriangle](API\Runtime\Engine\FClipSMTriangle) > & OutTris, [TArray](API\Runtime\Core\Containers\TArray)< [FUtilEdge3D](API\Runtime\Engine\FUtilEdge3D) > & OutClipEdges, const [TArray](API\Runtime\Core\Containers\TArray)< [FClipSMTriangle](API\Runtime\Engine\FClipSMTriangle) > & InTriangles, const FPlane & Plane ) }